JP4920221B2 - Optical semiconductor device having InP substrate - Google Patents

Description

The present invention relates to an optical semiconductor device having an InP substrate. In a compound semiconductor mainly composed of a group II element and a group VI element, the present invention relates to a p-type semiconductor cladding layer having a wide band gap but difficult to perform high concentration doping. An optical semiconductor having a p-type cladding layer and the like capable of obtaining a sufficient (1 × 10 ¹⁷ cm ⁻³ or more) p-type carrier concentration and a wide band gap by inserting a semiconductor layer capable of obtaining a high carrier concentration. Relates to the device.

  Further, the present invention relates to an optical element such as a semiconductor laser diode (LD), a light emitting diode (LED), a light receiving element (PD) using a p-type cladding layer by the above method, and is suitable for application to an optical apparatus.

  Semiconductor devices that emit light in the visible to ultraviolet range, that is, semiconductor lasers and light-emitting diodes, are used for optical information recording devices (compact discs (CD), digital versatile discs (DVD), Blu-ray discs (BD)), and light sources for color display devices. It is one of the important semiconductor devices in modern society / industry such as solid laser excitation, processing, sensor, measuring instrument, medical use, and white lamp application.

  As a semiconductor material for these optical elements, AlGa (In) As III-V group compounds have been used so far for infrared light devices such as 780 nm, 808 nm, 860 nm, 915 nm, and 980 nm bands. An AlGaInP III-V compound semiconductor is used as a material for a red light device having an emission wavelength of 600 nm band (especially 635 to 670 nm), and an AlGaInN III-V group nitride is used for a blue light device of 400 nm band (particularly 400 to 480 nm). Research and development has been advanced using physical semiconductors, and each has been put to practical use.

  However, regarding semiconductor devices that emit light from yellow to green in the 500 nm band, which is an intermediate wavelength band between red and blue, research and development as well as material development have not been sufficiently performed. For this reason, in particular, with regard to laser diodes, performance that can withstand practical use has not yet been realized.

II-VI group semiconductors are useful as semiconductors for these optical devices, as well as III-V group compound semiconductors. In general, however, p-type conductivity control is difficult, and p-type semiconductor layers of pn junction type semiconductor devices are made of ZnSe. It can be realized only with a limited type of II-VI semiconductors. In these II-VI group semiconductors, the p-type carrier concentration generally decreases as the forbidden band width becomes wider, and cannot be used for pn junction type semiconductor devices. For example, in ZnMgSSe lattice-matched to a GaAs substrate, the forbidden band width can be increased as the Mg composition ratio increases. However, when the forbidden band width is 3 eV or more, the p-type carrier concentration is as small as less than 1 × 10 ¹⁷ cm ^−3. Value. Similarly, a MgSe / ZnSeTe superlattice lattice-matched to an InP substrate can similarly obtain only a small p-type carrier concentration in a forbidden band width of 2.6 eV or more. (H. Okyama, Y. Kishita, T. Miyajima and A. Ishibashi, “Epitaxial growth of p-type ZnMgSe,” Appl. Phys. 94. 74. h. , I. Nomura, H. Shimbo, H. Hattori, T. Sano, Song-Bek Che, A. Kikuchi, K. Shimomura and K. Kishikino, “Growth and character. InP substrates and fabricati n of light emitting dioede, "Jpn. J. Appl. Phys., 38 (4B) 1999, see p.2598)
Under such circumstances, the inventors and several research groups in Japan and abroad can be produced by crystal growth on an InP semiconductor substrate as a candidate material for forming a semiconductor device that emits yellow to green light, and Research and development have been conducted focusing on Mg _x Zn _y Cd _1-xy SeII-VI group compound semiconductors lattice-matched to InP substrates (N. Dai et al. Appl. Phys. Lett., 66, 2742 (1995), And T. Morita et al., J. Electron. Mater., 25, 425 (1996)). In Mg _x Zn _y Cd _1-xy Se, each composition (x, y) is y = 0.47-0.37x (x = 0-0.8, y = 0.47-0.17). When the equation is satisfied, lattice matching with InP is performed, and the forbidden bandwidth is changed from 2.1 eV by changing the composition from (x = 0, y = 0.47) to (x = 0.8, y = 0.17). It has the feature of being able to control up to 3.6 eV.

Further, in the above composition range, all the forbidden bands show a direct transition type, and when the forbidden band width is converted into a wavelength, the wavelength is changed from 590 nm (dark blue) to 344 nm (ultraviolet). It has been suggested that the active layer and the clad layer for constituting the double hetero structure, which is the basic structure, can be realized only by changing the composition of Mg _x Zn _y Cd _1-xy Se.

Indeed, in the measurement of photoluminescence _{Mg x Zn y Cd 1-x} -y Se grown on an InP substrate by molecular beam epitaxy (MBE), in different _{Mg x Zn y Cd 1-x} -y Se compositions Good emission characteristics with a peak wavelength of 571 to 397 nm have been obtained (see T. Morita et al., J. Electron. Mater., 25, 425 (1996)).

In the laser structure using Mg _x Zn _y Cd _1-xy Se, laser oscillation by optical excitation has been reported in each of the red, green, and blue wavelength bands (L. Zeng et al. Appl. Phys. Lett., 72, 3136 (1998)).

On the other hand, laser oscillation by current drive of a semiconductor laser diode composed only of Mg _x Zn _y Cd _1-xy Se has not been reported so far. It is considered that the main reason why laser oscillation has not been obtained is that p-type conductivity control by impurity doping of Mg _x Zn _y Cd _1-xy Se is difficult.

The double heterostructure, which is the basic structure of a semiconductor laser diode, has a structure in which an active layer that generates light is n-type and p-type conductivity controlled and is sandwiched between clad layers having a wider forbidden band than the active layer. Yes. Here, it is clear from the above research report that Mg _x Zn _y Cd _1-xy Se has excellent properties as an active layer material.

In addition, n-type conductivity control of Mg _x Zn _y Cd _1-xy Se is obtained by doping with chlorine atoms, and an n-type carrier (electron) concentration of 1 × 10 ¹⁸ cm ⁻³ or more has been reported. (See W. Lin et al. Appl. Phys. Lett., 84, 1472 (1998).) However, with respect to p-type conductivity control, a p-type carrier of 1 × 10 ¹⁷ cm ⁻³ or more required for a laser diode. Concentration is not reported.

Conventionally, in order to control the p-type conductivity of II-VI group compound semiconductors, particularly ZnSe and MgZnSSe, a technique of doping high-energy radical nitrogen during crystal growth by molecular beam epitaxy has been mainly performed (RM). Park et al. Appl. Phys. Lett., 57, 2127 (1990) and K. Ohkawa et al. Jpn. J. Appl. Phys., 30, L152 (1991)). Thereby, a p-type carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or more has been reported (see H. Okuyama et al. Appl. Phys. Lett., 64, 904 (1994)).

Using a similar method, p-type conductivity control of Mg _x Zn _y Cd _1-xy Se has been attempted. However, in ZnCdSe having a composition (x = 0, y = 0.48), 3.5 × Only a p-type doping concentration of 10 ¹⁶ cm ⁻³ has been reported (see K. Naniwae et al., J. Cryst. Growth, 184/185, 450 (1998)). From higher concentration doping and also from ZnCdSe A p-type conversion with Mg _x Zn _y Cd _1-xy Se (x> 0) having a wide forbidden band has not been obtained.

The reason why the high p-type doping of Mg _x Zn _y Cd _1-xy Se is difficult is not clear, but at least some of the atoms arranged in the Mg _x Zn _y Cd _1-xy Se crystal It is thought that the cause is that the ideal impurity dopant that exists stably in the crystal and efficiently releases holes with low energy has not yet been found or does not exist. This is an essential characteristic / problem of Mg _x Zn _y Cd _1-xy Se.

  In JP-A-7-326817, a light-emitting device constituted by using a II-VI group compound semiconductor in order to increase the maximum p-type carrier concentration that can be taken by a clad layer having a wide band gap, It has been proposed that the mold cladding layer has a superlattice structure made of a material containing at least one element of Mg, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, and Ni. Characteristics are not obtained.

H. Okuyama, Y. Kishita, T. Miyajima and A. Ishibashi, “Epitaxial growth of p-type ZnMgSSe,” Appl. Phys. Lett., 64 (7) 1994, p.904. W. Shinozaki, I. Nomura, H. Shimbo, H. Hattori, T. Sano, Song-Bek Che, A. Kikuchi, K. Shimomura and K. Kishino, ”Growth and characterization of nitrogen-doped MgSe / ZnSeTe superlattice quasi -quaternary on InP substrates and fabrication of light emitting dioede, ”Jpn. J. Appl. Phys., 38 (4B) 1999, p.2598 N. Dai et al. Appl. Phys. Lett., 66 2742 (1995) T. Morita et al. J. Electron. Mater., 25 425 (1996) L. Zeng et al. Appl. Phys. Lett., 72 3136 (1998) W. Lin et al. Appl. Phys. Lett., 84 1472 (1998) R. M. Park et al. Appl. Phys. Lett., 57 2127 (1990) K. Ohkawa et al. Jpn. J. Appl. Phys., 30 L152 (1991) H. Okuyama et al. Appl. Phys. Lett., 64 904 (1994) K. Naniwae et al. J. Cryst. Growth, 184/185 450 (1998) JP 7-326817 A

Therefore, in order to realize an optical element such as a laser diode, a light emitting diode, and a light receiving element, the present invention has, for example, Mg _x Zn _y Cd _1-xy Se having a large energy gap that can be a cladding layer. in materials like becomes the normal case p-type conduction is the carrier concentration obtained only less than 1 × ¹⁰ 17 ^{cm -3,} providing a structure to obtain 1 × ¹⁰ 17 ^{cm -3} or more high p-type carrier concentration It is to be.

  Furthermore, the problem to be solved by the present invention is to provide a p-type semiconductor layer structure that can easily manufacture a semiconductor optical element and a device that have good characteristics such as light emission characteristics, reliability, and long life. is there.

The present inventor has intensively studied to solve the above problems. The outline will be described as follows. The present inventor has obtained a high p-type carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or more as a result of repeated improvements in the technology of semiconductor materials that could only be obtained with low p-type conductivity by the conventional method. The present inventors have succeeded in producing a p-type semiconductor layer with few crystal defects and excellent electrical conductivity and low resistance crystallinity.

  By making such a semiconductor layer possible and used for element fabrication, it has greatly contributed to the realization of optical elements and optical devices, such as laser diodes and light emitting diodes that emit light from yellow to green. Expected to do.

  First, the reason why the inventor used the InP substrate will be described. Conventionally, laser diodes that emit light in green, whose light emission characteristics, in particular, life characteristics, which have been researched and developed, have GaAs as a substrate, ZnCdSe as an active layer, and ZnMgSSe as an n-type cladding layer and a p-type cladding layer. Have been used.

In this structure, the forbidden band width can be increased with increasing Mg composition ratio in the ZnMgSSe of the p-type cladding layer. However, when the forbidden band width is 3 eV or more, the p-type carrier concentration is less than 1 × 10 ¹⁷ cm ^−3. Is a small value. At this time, even when N (nitrogen) serving as a dopant is contained in an atomic concentration of 1 × 10 ¹⁹ cm ⁻³ or more, the p-type carrier concentration becomes a small value of less than 1 × 10 ¹⁷ cm ⁻³ , that is, It can be said that the carrier activation rate is 1% or less. That is, N that does not become a p-type carrier becomes not only an interstitial atom entering the VI group site of ZnMgSSe but also an interstitial atom, that is, an interstitial defect.

  Furthermore, ZnCdSe, which is the light emitting region, is not lattice-matched with the GaAs substrate and has a larger lattice than GaAs. This means that ZnCdSe causes compressive strain.

  When a driving current is passed through the electrodes through these stacked structures, a group of crystal defects centered on interstitial defects existing in large amounts in the p-type ZnMgSSe cladding layer propagates and diffuses into the ZnCdSe active layer, which is a light-emitting region having compressive strain. As a result, a non-luminescent center is generated, and finally, heat is generated to stop light emission, leading to irreversible crystal breakage, and the lifetime ends.

  More generally, in semiconductor light emitting devices and light receiving devices, defects propagate and diffuse from the region with the most crystal defects due to the influence of heat, electrical conduction, strain, etc., and finally reach the light emitting region (active layer). As a result, the element deteriorates and the element life ends. When manufacturing a semiconductor optical element, it is necessary to eliminate or reduce the adverse effect of crystal defects on the element.

As a means for solving the problem, the inventor focused on the InP substrate and lattice-matched the active layer serving as the light emitting region, that is, using, for example, BeZnSeTe having substantially the same size and substantially no strain. . Furthermore, for the cladding layer, for example, MgZnCdSe having substantially the same lattice size and substantially no strain was adopted, and it was confirmed that the n-type conductivity was good. Next, when the p-type conduction was examined, the conventional N-type radical doping yielded a carrier concentration of less than 1 × 10 ¹⁷ cm ⁻³ . As a result of repeated studies, a technique for producing a p-type semiconductor layer having a high p-type carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or more, few crystal defects, and excellent electrical conductivity and low resistance crystallinity. In an optical semiconductor having a structure having an n-type clad layer, an active layer and a p-type clad layer on an InP substrate, the p-type clad layer is inserted into a first layer which is a main semiconductor layer. Thus, it is proposed that the carrier concentration of the p-type cladding layer be significantly improved by the holes supplied from the second layer.

In this invention comprised as mentioned above, it has a high p-type carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or more with respect to a semiconductor material in which only a low p-type conductivity was obtained by the conventional method, A semiconductor layer with few crystal defects and low resistance and excellent crystallinity can be manufactured.

  By making such a semiconductor layer possible and used for device fabrication, it is possible to fabricate semiconductor devices, laser diodes, and light emitting diodes that emit light from yellow to green, for example, which could not be realized conventionally.

  According to the present invention, an optical semiconductor device with higher practicality than before can be realized.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings of the embodiments, the same or corresponding parts are denoted by the same reference numerals.

Mg _x Zn _y Cd _1-xy Se is subjected to radical nitrogen doping, which has been performed in conventional II-VI group semiconductors (ZnSe and MgZnSSe), and its nitrogen flow rate, RF output, growth temperature, VI / II Even if the MBE growth conditions such as the ratio are optimized, the p-type carrier concentration is at most about 3.5 × 10 ¹⁶ cm ⁻³ , that is, less than 1 × 10 ¹⁷ cm ⁻³ , and is 1 × 10 ¹⁷ cm ⁻³ or more. A p-type carrier concentration could not be realized.

As a result of intensive studies, the inventor has been able to devise another doping technique.
In the present invention, in order to solve this problem, the first layer, for example, Mg _x Zn _y Cd _1-xy Se crystal is doped with a high concentration of p-type to about 10 ¹⁸ to 10 ²⁰ cm ⁻³ . 2 thin film semiconductor crystal layers were inserted at an appropriate interval, and a sufficient p-type carrier concentration could be obtained in the entire inserted semiconductor crystal.

  Here, differences between some known techniques and the present invention will be described. Japanese Patent Laid-Open No. 7-326817 discloses a p-type cladding in a light-emitting device using a II-VI group compound semiconductor for the purpose of increasing the maximum p-type carrier concentration that a clad layer having a wide band gap can take. It has been proposed that the layer has a superlattice structure made of a material containing at least one element of Mg, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, and Ni. Specifically, MgZnSSe and ZnSSe lattice-matched to a GaAs substrate are targeted. These points are clearly different from the concept of forming a p-type cladding layer by doping N into, for example, both typical MgZnCdSe and ZnSeTe on the InP substrate of the present invention.

  Next, W.W. Lin et al., Applied Physics Lett. Differences from the contents reported in the magazine (Vol. 76 (2000), page 2205) will be described. In order to increase the p-type carrier concentration of ZnSe, a method is described in which Te and N are made into a delta doping state after ZnSe is stacked. The present invention forms a p-type cladding layer on an InP substrate, for example by doping N into both typical MgZnCdSe and ZnSeTe (completely grown layer, not delta doping). Therefore, they are clearly different concepts.

Next, W.W. The difference from what Lin et al. Reported in Journal of Vacuum Science & Technology B (vol. 18 (2000) page 1534. p type of (Zn, Mg, Cd) Se on InP substrate. In order to increase the carrier concentration, a superlattice layer of (Zn, Mg, Cd) Se and a ZnSe layer having a carrier concentration of at most 1 × 10 ¹⁸ cm ^{−3 at} the highest in a single layer is laminated, and ZnSe In the present invention, a p-type cladding layer is formed on an InP substrate by doping N into, for example, both a typical MgZnCdSe and ZnSeTe (fully grown layer instead of delta doping). Therefore, they are clearly different concepts.

  Next, H.I. D. Jung et al., Applied Physics Lett. Differences from the contents reported in the magazine (Vol. 70 (1997), page 1143) will be described. In order to increase the carrier concentration of ZnSe, only ZnTe of one atomic layer or less is delta-doped with N and inserted into undoped ZnSe. The present invention forms a p-type cladding layer on an InP substrate, for example by doping N into both typical MgZnCdSe and ZnSeTe (completely grown layer, not delta doping). Therefore, they are clearly different concepts.

  The present invention provides an n-type cladding, an active layer, and an optical semiconductor device having this p-type cladding on an InP substrate by providing the unique p-type cladding described above. Hereinafter, this p-type cladding will be described.

FIG. 1 is a first conceptual schematic view of an embodiment of the present invention, schematically showing a structure according to the present invention, and a sectional view of a structure in which a specific layer is inserted into a host layer. The entire structure is p-type doped. For example, here, the main first semiconductor layer 1 (hereinafter referred to as a host layer) is Mg _x Zn _y Cd _1-xy Se (ZnCdSe when x = 0). Mg _x Zn _y Cd _1-xy Se has an energy gap from CdSe (1.764 eV) to MgSe (4.0 eV) by arbitrarily setting the composition ratio x and y, and from ZnSe (5.668Å). A semiconductor layer having a lattice constant of up to CdSe (6.057Å) can be formed.

In the embodiment of the present invention, a host layer Mg _x Zn _y Cd _1-xy Se lattice-matched to a widely existing InP substrate (5.869８６) (may be ZnCdSe when x = 0) is used. Use. By growing the semiconductor layer in lattice matching, a high-quality semiconductor layer having substantially no distortion and few crystal defects can be obtained.

More specifically, the Mg _x Zn _y Cd _1-xy Se layer lattice-matched to InP is, in particular, the composition ratio (x, y) of the Mg _x Zn _y Cd _1-xy Se layer is y. = 0.47-0.37x (x = 0-0.8, y = 0.47-0.17) satisfying the relational expression, the composition ratio is (x = 0, y = 0.47) It is a compound semiconductor layer in the range of (x = 0.8, y = 0.17).

In FIG. 1, the second layer 2 (hereinafter referred to as a specific layer) inserted between the host layer Mg _0.5 Zn _0.29 Cd _0.21 Se layer (10 ML (atomic layer) thickness) 1 lattice-matched to the InP substrate. ZnSe _0.53 Te _0.47 layer (2 ML) is inserted.

FIG. 2 is a diagram showing the relationship between the lattice constant and the energy gap (forbidden band width) relating to the main material of the present invention. The lattice-matching portion of InP corresponds to the dotted line. For example, by setting the composition ratio x and y of Mg _x Zn _y Cd _1-xy Se in a triangle surrounding ZnSe, CdSe, and MgSe, MgZnCdSe having an arbitrary lattice constant and energy gap is manufactured. Can do.

Further, in FIG. 2, a line segment connecting ZnSe and ZnTe is drawn, and a composition ratio z of ZnSe _z Te _1- z is set to produce ZnSe _0.53 Te _0.47 lattice-matched to InP. Can do.

In the sample structure produced as shown in FIG. 1, the Mg _0.49 Zn _0.29 Cd _0.22 Se layer of the host layer 1 has an energy gap of 2.95 eV, and the ZnSe _0.53 Te _{0. When 47} layers were inserted at 0.59 nm and the p-type carrier concentration was measured, a carrier concentration of 2.1 × 10 ¹⁸ cm ⁻³ was obtained.

In FIG. 1, the specific layer 2 to be inserted is a ZnSe _0.53 Te _0.47 layer lattice-matched to InP. However, ZnTe and BeTe not lattice-matched, ZnSeTe not lattice-matched, and lattice-matched are not. MgZnSeTe and BeZnTe which are not related may be used. When lattice matching is not achieved, misfit dislocation occurs when the film thickness exceeds the critical thickness due to the magnitude of the deviation. For this reason, it is necessary to make it below the critical film thickness below several atomic layers.

It has been experimentally shown that the semiconductor layer that can be the specific layer 2 can obtain a high p-type carrier concentration of 10 ¹⁸ cm ⁻³ or more by radical nitrogen doping (for ZnTe, IW Tao et al. Appl. Phys., Lett., 64, 1848 (1994), for ZnSeTe, see W. Shinozaki et al. Jpn. J. Apll. Phys., 38, 2598 (1999), for MgZnSeTe, et al., Appl. , 65, 3215 (1994), and regarding BeZnTe, see SB Che, J. Cryst. Growth, 214/215, 321 (2000)). Here, ZnSeTe, MgZnSeTe, and BeZnTe other than ZnTe and BeTe can be lattice-matched to InP, and when these are inserted into a host crystal as a highly doped crystal, a high-quality crystal lattice-matched to the InP substrate as a whole crystal is obtained. It is done.

  The host layer 1 shown in FIG. 1 is MgZnCdSe, but may be an MgZnSeTe layer. Also, a BeZnCdSe layer and a BeZnSeTe layer may be used, but in this case, since the energy gap is 2.6 eV or less and 2.8 eV or less, for example, when manufacturing an optical element or the like, the energy gap numerical value of the active layer is set. Therefore, it is necessary to determine whether it is effective for carrier confinement in consideration of design and manufacture.

  The layer thicknesses of the host layer 1 and the specific layer 2 shown in FIG. 1 are repeated several times with the layer thickness of the host layer and the specific layer being constant, but the thickness of the host layer and the specific layer is aperiodic. Alternatively, it may be set at random. For example, the MgZnCdSe layer of the host layer 1 has an energy gap of 2.95 eV, the ZnSeTe layer of the specific layer 2 is inserted by 1 ML thickness, the MgZnCdSe layer of the host layer is then stacked, and then the ZnSeTe layer of the specific layer is inserted by 2 ML thickness Then, the layer thickness of the specific layer after the host layer is further laminated may be 3 ML.

FIG. 3 shows a second conceptual schematic diagram of the embodiment of the present invention. Here, the host layer 11 is a MgSe / ZnCdSe superlattice. The MgSe / ZnCdSe superlattice has a structure in which MgSe thin film crystals and ZnCdSe thin film crystals are alternately stacked. By changing the thickness of each layer to several nanometers to several nanometers, which is less than the electron de Broglie wavelength, It can be regarded as a typical Mg _x Zn _y Cd _1-xy Se mixed crystal. The entire structure is p-type doped.

  In addition, since the lattice constant (5.91Å) of MgSe is close to the lattice constant (5.869Å) of InP, and ZnCdSe can be lattice-matched to InP, the MgSe / ZnCdSe superlattice can be fabricated by being pseudo-lattice-matched to InP. Good quality crystals are obtained.

In the MgSe / ZnCdSe superlattice, physical parameters such as a forbidden band width can be controlled while changing the thickness of each layer of MgSe and ZnCdSe while lattice matching with InP. This is because Mg _x Zn _y Cd _1-xy Se There is an effect equivalent to changing the composition (x, y).

In _{fact, Mg x Zn y Cd 1-} x-y than varying the composition of Se is better to change the layer thickness of the MgSe / ZnCdSe superlattice is remarkably easier in terms of crystal growth, MgSe / ZnCdSe superlattice semiconductor It is a very effective material for fabricating a complex heterostructure in a device (see H. Shimbo et al., J. Cryst. Growth, 184/185, 16 (1998)).

On the other hand, although the specific layer 12 to be inserted is ZnSeTe in FIG. 3, it may be ZnTe, BeTe, MgZnSeTe, or BeZnTe. It has been experimentally shown that these crystals can obtain a high p-type carrier concentration of 10 ¹⁸ cm ⁻³ or more by radical nitrogen doping (for ZnTe, IW Tao et al. Appl. Phys. Lett., 64, 1848 (1994), for ZnSeTe, see W. Shinozaki et al., Jpn. J. Apll. Phys., 38, 2598 (1999), and for MgZnSeTe, W. Faschinger et al., Appl. See, SB Che, J. Cryst. Growth 214/215, 321 (2000) for BeZnTe).

  Here, ZnSeTe, MgZnSeTe, and BeZnTe other than ZnTe and BeTe can be lattice-matched to InP, and when these are inserted into a host crystal as a highly doped crystal, a high-quality crystal lattice-matched to the InP substrate as a whole crystal is obtained. It is done.

  On the other hand, since ZnTe has a lattice constant of 6.10Å and a lattice mismatch of + 3.9% compared to InP (lattice constant: 5.869Å), the host crystal in which ZnTe is lattice-matched to the InP substrate is used. Insertion may cause defects due to crystal distortion. However, by making the ZnTe layer thickness below the critical thickness where misfit dislocations do not occur, and by making the lattice constant of the host crystal layer intentionally smaller than that of InP and making it negative lattice mismatch, This can be solved by using a so-called net zero distortion. Here, the condition for net zero distortion can be expressed by equation (1).

  From this, for example, when ZnTe is a highly doped layer and the layer thickness ratio is 0.1, it is required that the crystal strain of the host layer be −0.433% in order to obtain net zero strain. Is possible by composition control in ZnCdSe and MgZnCdSe. Thus, even when ZnTe having a large lattice strain is used, a high-quality crystal can be obtained by using the technique of net zero strain.

  In FIG. 3, the host layer 11 is an MgSe / ZnCdSe superlattice layer, but MgZnSe or MgZnSeTe may be used instead of MgSe.

  Furthermore, in FIG. 3, the host layer 11 is an MgSe / ZnCdSe superlattice layer, but ZnSeTe, BeZnCdSe, BeZnSeTe, MgZnCdSe, and MgZnSeTe may be used instead of ZnCdSe.

In the present invention, p-type carriers (holes) are emitted from the specific layer 12 to the host layer 11 by inserting the specific layer 12 into the host layer 11 at an appropriate interval, and the total crystal is 10 ¹⁷ cm ^−3. A sufficient hole concentration as described above can be obtained. Here, the specific layer 12 is thinner than the host layer 11 and has a small proportion of the entire crystal. Therefore, the insertion of the specific layer 12 has little effect on physical parameters such as the energy gap of the host layer 11. None or minimal.

  In general, a p-type doped semiconductor has an acceptor level formed in the vicinity of the upper end of its valence band, and holes are emitted therefrom to exhibit p-type conductivity. Here, there are two possible mechanisms for obtaining p-type doping according to the present invention. The conceptual diagram is shown in FIGS. 4 (a) and 4 (b). 4A and 4B schematically show a valence band structure of a semiconductor in which a specific layer is inserted into a host layer. It is a figure explaining the theoretical basis of this invention, and is a model which shows the valence band structure of the quantum well which inserted the specific layer in the host layer, the p-type carrier (hole) which exists there, its wave function, and an energy level FIG. Here, A: valence band structure of quantum well structure by host crystal and highly doped crystal, B: energy quantum level in quantum well of p-type carrier (hole), C: p-type carrier (hole), D : Shows the wave function of p-type carriers (holes) confined in the quantum well.

  As shown in FIGS. 4 (a) and 4 (b), in the combination of the host layer and the specific layer, the valence band structure has a well layer as the specific layer because of the band lineup of the semiconductor crystals. A so-called quantum well structure in which the host layer becomes a barrier layer is formed. Further, the thickness of the specific layer to be inserted is about several to several nanometers, and the quantum level of holes is formed in the quantum well as shown in FIGS. 4 (a) and 4 (b). The

As shown in FIG. 4 (a), as the first mechanism for obtaining p-type by the present invention, holes are thermally excited from the high concentration acceptor in the specific layer to the valence end of the host layer, Since it behaves as a free carrier (hole), it is considered that the p-type can be obtained as a whole. At this time, the concentration of holes excited to the valence edge of the host crystal is approximately proportional to exp (−Ea / kT). In the above equation, Ea is the activation energy, k is the Boltzmann constant, and T is the absolute temperature. Here, it is considered that the hole concentration to be excited decreases compared to the specific layer because the activation energy increases corresponding to the energy of the barrier layer compared to the specific layer which is a well layer. For example, if the increase in activation energy is 0.12 eV, the hole concentration at room temperature (T = 300K) is estimated to decrease to about 1/100. However, if the hole concentration of high doping is 10 ²⁰ cm ⁻³ , the excited hole concentration is 10 ¹⁸ cm ⁻³ , and it is expected that a value sufficient for application to a device can be obtained. Therefore, p-type conversion by this mechanism is considered effective when the height (energy) of the well barrier between the host layer and the specific layer is about 0.12 eV or less.

  As the second mechanism, as shown in FIG. 4B, the wave function of holes confined in each well layer overlaps with the wave function in the adjacent well layer to form a miniband. It can be considered that p-type conversion is exhibited by holes excited in the band. In this case, the limitation on the height of the well barrier in the first mechanism is relaxed, and a high hole concentration is expected if the energy level of the miniband formed in the deeper well structure is sufficiently low. The energy level of the miniband can be artificially controlled within a range determined by the thickness of the well layer and the barrier layer.

  A first embodiment of the present invention will be described. The sample shown in FIG. 5A is manufactured and the characteristics are evaluated.

It is produced by crystal growth using a two-growth chamber molecular beam epitaxy (MBE) apparatus. First, after an optimal surface treatment is performed on the InP substrate 21, it is set in the MBE apparatus. It puts in the preparation room for sample exchange, and it evacuates to 10 < ^-3 > Pa or less with a vacuum pump, It heats to 100 degreeC and desorbs a residual moisture and impurity gas.

  Next, the substrate is transported to a group III-V dedicated growth chamber, and the substrate temperature is heated to 500 ° C. while applying a P molecular beam to the substrate surface to remove the oxide film on the substrate surface. The buffer layer 22 is grown to a thickness of 30 nm, and the InGaAs buffer layer 23 is grown to a thickness of 0.1 μm at a substrate temperature of 470 ° C.

  Next, the sample is transported to the II-VI group growth chamber, Zn molecular beam irradiation and growth of the ZnCdSe low-temperature buffer layer 24 (layer thickness 5 nm) are performed at a substrate temperature of 200 ° C., and then ZnCdSe buffer is applied at a substrate temperature of 280 ° C. Layer 25 (layer thickness 100 nm), MgSe / ZnCdSe superlattice 26 (MgSe layer thickness is 0.6 nm, ZnCdSe layer thickness is 1.71 nm, period is 57 pairs, total layer thickness is 0.13 μm) After the lamination, a superlattice structure 28 (total thickness of 0.5 μm) was formed by combining the host layer according to the present invention and the specific layer to be inserted, and finally a ZnTe layer 30 (5 nm) was laminated. Here, the superlattice structure 28 is a ZnCdSe / ZnTe superlattice structure in which the host layer is ZnCdSe, the specific layer is ZnTe, and 110 pairs of ZnCdSe layers having a thickness of 3.96 nm and ZnTe thin film layers having a thickness of 0.73 nm are alternately stacked. It was. At that time, the superlattice structure 28 was grown while performing radical nitrogen doping under the conditions of a nitrogen flow rate of 0.015 sccm, an RF output of 400 W, a growth temperature of 280 ° C., and a VI / II ratio of about 1.

Incidentally, as a result of measuring the p-type carrier concentration of a sample obtained by growing a ZnTe single layer film by radical nitrogen doping under the same conditions in a preliminary experiment performed prior to this experiment, the result was 5 × 10 ²⁰ cm ⁻³ . High concentration doping has been confirmed.

  Next, a Schottky type two electrode 31 as shown in FIG. 5A is formed by vapor deposition of Ti and Al and patterning by resist and light exposure. The capacitance-voltage (CV) method measurement at room temperature was performed using this electrode, and the effective acceptor (p-type doping) concentration in the ZnCdSe / ZnTe superlattice layer was determined.

The relationship between the obtained effective acceptor concentration and the ZnTe layer thickness is shown in FIG. Here, when the ZnTe layer thickness is 0, literature values for a nitrogen-doped ZnCdSe single layer film (see K. Naniwae et al., J. Cryst. Growth, 184/185, 450 (1998)) are shown. As can be seen from FIG. 6, the effective acceptor concentration of the ZnCdSe monolayer film was as low as 3.5 × 10 ¹⁶ cm ⁻³ , whereas the insertion of a ZnTe thin film resulted in a high carrier concentration of 8 × 10 ¹⁷ cm ^−3. was gotten.

When the layer thickness of the specific layer ZnTe of the superlattice structure 28, which is a ZnCdSe / ZnTe superlattice layer, was set to 0.29 nm and 0.59 nm, and the same structure as FIG. 5A was fabricated and evaluated, each was 1.9 × 10 ¹⁷ cm. ⁻³ and 3.1 × 10 ¹⁷ cm ⁻³ .

That is, when the ZnTe layer thickness is 0.73 nm, it is 8 × 10 ¹⁷ cm ⁻³ , and 20 times or more high concentration doping is achieved compared to the p-type ZnCdSe single layer film 3.5 × 10 ¹⁶ cm ^−3. It was done. Higher concentrations can also be expected by optimizing growth conditions.

  Furthermore, by using ZnSeTe, which has a smaller electron band energy discontinuity value than ZnTe, for the specific layer of the superlattice structure 28, carriers from the specific layer can be easily extracted, and the resistance of the P-type cladding can be reduced. Can be reduced.

  In addition, the effective acceptor concentration of the superlattice structure 28 with the laminated structure of the host layer and the specific layer having a constant film thickness has been shown so far. The results of FIG. 6 show that the film thicknesses of both layers are random or regularly. This suggests that it can be applied to a film thickness modulation structure that changes. Such application examples are shown below.

  FIG. 5B is a diagram illustrating an application example to a film thickness modulation structure that is regularly changed. A specific layer (for example, ZnTe, 0.29 nm, 0.56 nm, 0.73 nm) with different thicknesses is appropriately applied to a host crystal (for example, ZnCdSe, thickness 3.96 nm) of the superlattice structure 28. By sequentially laminating several layers, a carrier concentration gradient can be provided while maintaining a high carrier concentration in the film thickness direction. As a result, the laser element can be applied such as having a degree of freedom in design regarding optical confinement and carrier absorption loss. In FIG. 5B, other configurations are the same as those in FIG. 5A.

  Another application example is shown in FIGS. 7A (b)-(d). Here, FIG. 7A (a) is a diagram showing a specific example of the superlattice structure 28 shown in FIG. 5A for comparison. The host layer is MgZnCdSe and the specific layer is ZnTe. The film thickness of the specific layer is 3 ML (atomic layer).

  In FIG. 7A (b), a specific layer having a thickness of 3 ML is divided into three thin film layers having a thickness of 1 ML, and the MgZnCdSe layer of the host layer is formed between these layers with the same or thicker thickness. This is an example. By reducing the thickness of the host layer (MgZnCdSe) used for the division (for example, 2 ML), the energy position of the miniband formed between the specific layers can be controlled. Compared to the quantum level according to the configuration of FIG. 7A (a), the position of the miniband can be brought closer to the valence band of the host layer, and holes in the specific layer can be more easily taken out to the host layer. The resistance of the P-type cladding composed of the specific layer and the host layer can be reduced.

  FIG. 7A (c) shows an example in which an intermediate layer (MgZnCdSeTe) whose composition changes continuously at the interface between the specific layer (ZnTe) having a thickness of 3 ML and the host layer (MgZnCdSe) is introduced. With this structure, hole movement in a direction perpendicular to the stacking direction can be improved, and the resistance of the p-type cladding according to the present invention can be reduced. This effect can also be obtained by a structure using a film thickness modulation superlattice structure at the intermediate portion between the specific layer and the host layer as shown in FIG. 7A (d). That is, in the example of FIG. 7A (d), a specific layer (ZnTe) having a thickness of 1 ML from the host layer (MgZnCdSe), a host layer (MgZnCdSe) having a thickness of 2 ML, a specific layer (ZnTe) having a thickness of 2 ML, By sequentially laminating the host layer (MgZnCdSe) with a thickness of 1 ML and laminating the specific layer with a thickness of 3 ML, the composition continuously changes at the interface between the specific layer (ZnTe) and the host layer (MgZnCdSe). A layer equivalent to the intermediate layer was constructed. The advantage of this structure is that crystal growth is easy because the entire P-type cladding is formed by using two types of crystals of the host layer and the specific layer. Here, the thickness of the layer having the same composition as the specific layer is sequentially reduced from the specific layer toward the host layer, and at the same time, the thickness of the layer having the same composition as the host layer is decreased from the specific layer to the host layer. The thickness is gradually increased toward. As a result, the film thickness modulation superlattice in the intermediate portion acts as a pseudo-mixed crystal, and acts as a layer having a band structure that is effectively equivalent to the intermediate layer whose composition continuously changes at the interface. As a result, the resistance of the P-type cladding layer can be reduced as in FIG. 7A (c). Here, a film thickness modulation superlattice composed of four layers is shown, but a film thickness modulation superlattice intermediate layer composed of more layers can also be used.

  FIG. 7B (a)-(d) is a figure which shows the energy with respect to the lamination direction obtained by the laminated structure in FIG. 7A (a)-(d), respectively. In FIG. 7B (b), compared with the quantum level (shown by a one-dot chain line) in FIG. 7B (a), holes in a specific layer can be more easily formed by bringing the position of the miniband closer to the valence band of the host layer. It can be taken out to the host layer, and the resistance of the P-type cladding composed of the specific layer and the host layer can be reduced. In FIG. 7B (d), it works effectively as a layer having a band structure as indicated by a one-dot chain line in the figure. As a result, the resistance of the p-type cladding layer can be reduced as in FIG. 7B (c).

  Next, a second embodiment of the present invention will be described. The samples shown in FIGS. 8A and 8B are manufactured and their characteristics are evaluated.

First, the sample shown in FIG. It is produced by crystal growth using a two-growth chamber molecular beam epitaxy (MBE) apparatus. First, after an optimal surface treatment is performed on the InP substrate 21, it is set in the MBE apparatus. It puts in the preparation room for sample exchange, and it evacuates to 10 < ^-3 > Pa or less with a vacuum pump, It heats to 100 degreeC and desorbs a residual moisture and impurity gas.

  Next, the substrate is transported to a group III-V growth chamber, and the substrate temperature is heated to 500 ° C. while applying a P molecular beam to the substrate surface to remove the oxide film on the substrate surface. The layer 22 is grown to a thickness of 30 nm, and the InGaAs buffer layer 23 is grown to a thickness of 0.1 μm at a substrate temperature of 470 ° C.

  Next, the sample is transported to a II-VI group growth chamber, Zn molecular beam irradiation and ZnCdSe low-temperature buffer layer 24 (layer thickness 5 nm) are grown at a substrate temperature of 200 ° C., and then ZnCdSe buffer layer 25 at a substrate temperature of 280 ° C. (Layer thickness 100 nm) is grown. Next, four layers of ZnTe layer 34 (0.73 nm) / ZnCdSe layer 35 (1.98 nm) / MgSe layer 36 (0.59 nm) / ZnCdSe layer 35 (1.98 nm) (shown as U1 in the figure) 110 pairs were stacked as one cycle. This superlattice structure was p-type doped with radical nitrogen under the conditions described above. Here, the host layer is a superlattice layer having a three-layer structure of ZnCdSe layer / MgSe layer 36 / ZnCdSe layer 35, and the specific layer is the ZnTe layer 34.

Incidentally, in a preliminary experiment conducted prior to this experiment, the p-type carrier concentration of a sample obtained by growing a ZnTe single layer film while performing radical nitrogen doping under the same conditions as described above was measured, and the result was 5 × 10 ²⁰ cm ⁻³ . High concentration doping has been confirmed.

  Next, a Schottky type two electrode 31 as shown in FIG. 8A is formed by deposition of Ti and Al and patterning by resist and light exposure. The capacitance-voltage (CV) method measurement at room temperature was performed using this electrode, and the effective acceptor (p-type doping) concentration in the MgSe / ZnCdSe / ZnTe superlattice layer was determined.

  FIG. 9 is a graph showing the relationship between the effective acceptor concentration of the MgSe / ZnCdSe / ZnTe superlattice and the MgSe layer thickness in one period of the superlattice in the second embodiment of the present invention. Here, the MgSe layer thickness is the total layer thickness of the MgSe layers in one period of the superlattice. Plot (a) in FIG. 9 is the above evaluation result. The case where the MgSe layer thickness in FIG. 9 is 0 is the case of the ZnCdSe (layer thickness 3.96 nm) / ZnTe (layer thickness 0.73 nm) superlattice in the first embodiment.

  A sample in which only the thickness of the MgSe layer 36 was increased from 0.59 nm to 1.17 nm with the configuration shown in FIG. 8A was added and added as a plot (b) in FIG.

Next, the sample shown in FIG. 8B will be described. This is a modification of the second embodiment, and this characteristic is added as a plot (c) in FIG. It is produced by crystal growth using a two-growth chamber molecular beam epitaxy (MBE) apparatus. First, after an optimal surface treatment is performed on the InP substrate 21, it is set in the MBE apparatus. It puts in the preparation room for sample exchange, and it evacuates to 10 < ^-3 > Pa or less with a vacuum pump, It heats to 100 degreeC and desorbs a residual moisture and impurity gas.

  Next, the substrate is transported to a group III-V growth chamber, and the substrate temperature is heated to 500 ° C. while applying a P molecular beam to the substrate surface to remove the oxide film on the substrate surface. The layer 22 is grown to a thickness of 30 nm, and the InGaAs buffer layer 23 is grown to a thickness of 0.1 μm at a substrate temperature of 470 ° C.

  Next, the sample is transported to a II-VI group growth chamber, Zn molecular beam irradiation and ZnCdSe low-temperature buffer layer 24 (layer thickness 5 nm) are grown at a substrate temperature of 200 ° C., and then ZnCdSe buffer layer 25 at a substrate temperature of 280 ° C. (Layer thickness 100 nm) is grown. Next, ZnTe layer 41 (0.73 nm) / ZnCdSe layer 42 (1.03 nm) / MgSe layer 43 (0.88 nm) / ZnCdSe layer 44 (1.91 nm) / MgSe layer 43 (0.88 nm) / ZnCdSe layer Sixty-two pairs of 42 (1.03 nm) (indicated as U2 in the figure) were stacked as one cycle, and finally a ZnTe layer 30 (5 nm) was stacked. That is, the host layer is a MgSe / ZnCdSe superlattice layer, and the specific layer is a ZnTe layer. The conditions described above were used for p-type doping with radical nitrogen.

  A sample in which only the thickness of the MgSe layer 43 was increased from 0.88 nm to 1.17 nm with the configuration shown in FIG. 8B was created and added as a plot (d) in FIG.

From FIG. 9, it is understood that an effective acceptor concentration of 4 × 10 ¹⁷ cm ⁻³ or more can be obtained at any MgSe layer thickness. On the other hand, increasing the MgSe layer thickness decreases the effective acceptor concentration. Here, the effective acceptor concentration regarding a laminated structure including a host layer having a certain film thickness and a specific layer is shown, but the result of FIG. 9 also suggests application to a film thickness modulation structure. That is, the same modification as the modification of FIG. 5B and FIGS. 7B to 7D can be made to the configuration of FIG. 5A. For example, a structure in which superlattice host layers having different thicknesses are sequentially laminated at an appropriate period between specific layers of ZnTe (eg, 0.29 nm, 0.56 nm, 0.73 nm) having a constant thickness is also possible. This makes it possible to provide a carrier concentration gradient while maintaining a high carrier concentration in the film thickness direction. Furthermore, the present invention can be applied by arbitrarily changing the thickness and composition of the host layer and the specific layer. As a result, a tilted superlattice structure using a composition-change intermediate layer and a tilted superlattice structure using a pseudo mixed crystal intermediate layer in which the thicknesses of the host layer and specific layer are continuously changed are fabricated. Can do.

Next, the surface reflectance spectra of these samples were measured, the light absorption edge was obtained therefrom, and the energy gap (forbidden band width) was estimated. FIG. 10 is a graph showing the relationship between the forbidden band width of the MgSe / ZnCdSe / ZnTe superlattice and the MgSe layer thickness in one period of the superlattice in the second embodiment of the present invention. The dependence of the forbidden band width on the MgSe layer thickness was shown. By increasing the MgSe layer thickness from 0 to 2.34 nm, the forbidden band width increased from 2.08 eV to 2.56 eV, and it was confirmed that the forbidden band width was increased by inserting the MgSe layer. Thus, even if the forbidden band width is increased to 2.56 eV by inserting the MgSe layer, a p-type carrier concentration of 4.5 × 10 ¹⁷ cm ⁻³ or more is obtained.

Next, a third embodiment will be described. The sample shown in FIG. 11 is manufactured and the characteristics are evaluated. It is produced by crystal growth using a two-growth chamber molecular beam epitaxy (MBE) apparatus. First, an optimal surface treatment is performed on the S-doped InP substrate 21 and then set in the MBE apparatus. It puts in the preparation room for sample exchange, and it evacuates to 10 < ^-3 > Pa or less with a vacuum pump, It heats to 100 degreeC and desorbs a residual moisture and impurity gas.

  Next, the substrate is transported to a group III-V growth chamber, and the substrate temperature is heated to 500 ° C. while applying a P molecular beam to the substrate surface to remove the oxide film on the substrate surface. The layer 21 is grown to a thickness of 30 nm, and the InGaAs buffer layer 23 is grown to a thickness of 0.1 μm at a substrate temperature of 470 ° C.

  Next, the sample is transported to a II-VI group growth chamber, Zn molecular beam irradiation and ZnCdSe low-temperature buffer layer 24 (layer thickness 5 nm) are grown at a substrate temperature of 200 ° C., and then ZnCdSe buffer layer 25 at a substrate temperature of 280 ° C. After sequentially laminating (layer thickness 100 nm), a superlattice structure was formed by combining the host layer 45 and the specific layer 46 to be inserted according to the present invention, and finally a ZnTe layer 30 (5 nm) was laminated. Here, the MgZnCdSe / ZnTe superlattice structure in which the host layer 45 is MgZnCdSe, the specific layer 46 is ZnTe, and 150 pairs of MgZnCdSe layers 45 having a thickness of 4.0 nm and ZnTe thin film layers 46 having a thickness of 1.0 nm are alternately stacked. did. The conditions described above were used for p-type doping with radical nitrogen.

Incidentally, in a preliminary experiment conducted prior to this experiment, the p-type carrier concentration of a sample obtained by growing a ZnTe single layer film while performing radical nitrogen doping under the same conditions as described above was measured, and the result was 5 × 10 ²⁰ cm ⁻³ . High concentration doping has been confirmed.

  Next, a Schottky type two electrode 31 as shown in FIG. 5A is formed by deposition of Ti and Al and patterning by resist and light exposure. The capacitance-voltage (CV) method measurement at room temperature was performed using this electrode, and the effective acceptor (p-type doping) concentration in the MgZnCdSe / ZnTe superlattice layer was determined.

The relationship between the obtained effective acceptor concentration and the energy gap is shown in FIG. 2.25 eV is the case of ZnCdSe / ZnTe. As can be seen from FIG. 12, although the carrier concentration slightly decreases as the energy gap increases, the carrier is as high as 2.1 × 10 ¹⁸ cm ^{−3 in the} MgZnCdSe / ZnTe superlattice semiconductor layer having a high energy gap of 2.95 eV. Concentration is obtained. The ZnCdSe single layer shown for reference was 3.5 × 10 ¹⁶ cm ⁻³ , and a P-type layer could not be obtained in a large band cap region. This clearly shows the effectiveness of the present invention aimed at achieving both wide band cap and high P-type doping.

Next, a fourth embodiment will be described. The semiconductor LD structure shown in FIG. 13A is fabricated. It is produced by crystal growth using a two-growth chamber molecular beam epitaxy (MBE) apparatus. First, after an optimal surface treatment is performed on the InP substrate 21, it is set in the MBE apparatus. It puts in the preparation room for sample exchange, and it evacuates to 10 < ^-3 > Pa or less with a vacuum pump, It heats to 100 degreeC and desorbs a residual moisture and impurity gas.

  Next, the substrate is transported to a group III-V growth chamber, and the substrate temperature is heated to 500 ° C. while applying a P molecular beam to the substrate surface to remove the oxide film on the substrate surface. The layer 22 is grown to a thickness of 30 nm, and the Si-doped n-type InGaAs buffer layer 53 is grown to a thickness of 200 nm at a substrate temperature of 470 ° C.

  Next, the sample was transported to a II-VI group growth chamber, Zn molecular beam irradiation and Cl-doped n-type ZnCdSe low temperature buffer layer 54 (layer thickness 5 nm) were grown at a substrate temperature of 200 ° C., and then at a substrate temperature of 280 ° C. Cl-doped n-type ZnCdSe buffer layer 55 (layer thickness 100 nm), Cl-doped n-type MgZnCdSe cladding layer 47 (layer thickness 800 nm), MgZnCdSe barrier layer 48, BeZnCdSe quantum well active layer 49 (layer thickness 7.5 nm), MgZnCdSe barrier layer 48 are sequentially stacked, and then a p-clad layer having an N-doped p-type superlattice structure is formed by combining the host layer MgZnCdSe45 and the specific layer ZnTe46 to be inserted according to the present invention, and an N-doped p-type ZnSeTe / ZnTe contact layer 50 (all Layer thickness 500nm) and finally N-doped p-type ZnTe Were sequentially laminated cap layer 30 (thickness 30 nm). Here, the MgZnCdSe / ZnTe superlattice structure in which 150 pairs are alternately stacked with the host layer 45 being MgZnCdSe (layer thickness: 4.0 nm) and the specific layer 46 being ZnTe (layer thickness: 1.0 nm).

  FIG. 13B is a diagram showing energy in the stacking direction obtained by the stacked structure in FIG. 13A.

  Next, a general procedure for forming individual optical semiconductor devices from the epitaxial wafer configured as described with reference to FIG. 13 will be described with reference to FIGS.

  14A, reference numeral 100 denotes the epitaxial wafer shown in FIG. 13, which includes a light emitting portion having a thickness of several μm shown in 101 and a base portion having a thickness of several hundred μm shown in 102. After a resist pattern (not shown) having a predetermined shape is formed by lithography on the p-type ZnTe cap layer 30 on the uppermost surface of the light emitting unit 101 to cover the surface of the portion other than the stripe portion and the current confinement region, A Pd film, a Pt film, and an Au film are sequentially vacuum deposited. Thereafter, the resist pattern is lifted off together with the Pd film, Pt film and Au film formed thereon. As a result, a p-type electrode made of Pd / Pt / Au is formed on the ZnTe contact layer 30. Thereafter, heat treatment is performed as necessary to make ohmic contact.

  On the other hand, as shown in FIG. 14B, the n-type InP substrate of the base portion 102 is thinned to about 100 μm, and an n-type electrode such as Au / Ge is vapor-deposited to make ohmic contact. As a result, a wafer 103 having electrodes formed on the upper and lower surfaces and both surfaces is obtained.

Next, as shown in FIG. 14 (c), 103a, 103b, 103b, 103b, 103b, 103b, 103d, 103d, 103d, 103d, 103d, 103d, 103d, 103d, 103d, 103d, 103d, 103d, and 103d are formed by scratching the edge of the wafer 103 with a diamond cutter 104, Cleave as shown by ----. Next, a low reflection coating of about 5% is formed on the front end surface that emits light and a high reflection coating of about 95% is formed on the rear end surface by vapor deposition or sputtering using Al ₂ O ₃ , SiO _x , SiN _x or the like. Next, a pelletizing process is performed in which the stripe direction is again set in the stripe direction, and the chip 105 can be obtained as shown in FIG.

  Next, as shown in FIG. 15A, the obtained chip 105 is placed on the Si submount 106 while adjusting the position of the light emitting point and the angle of the end face. Solder is applied between the Si submount 106 and the chip 105, and heat is applied to fix the solder in an alloy process in which the solder is melted. Next, as shown in FIG. 15B, the Si wafer is cut by a dicer and separated individually as shown as 106a. Next, a die-bonding process for bonding onto the heat sink stem 107 made of copper or the like is performed, and fixed by a heating process using solder or an adhesive. Next, as shown in FIG. 15C, a wire bonding step is performed in which the electrode on the chip 105 and the terminal on the heat sink stem 107 are connected by a gold wire. Next, as shown in FIG. 15D, a window cap 108 serving as an exit of the laser beam is subjected to a sealing process using welding to the heat sink stem, thereby completing a final package. .

  As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to the above-mentioned embodiment, The various deformation | transformation based on the technical idea of this invention is possible.

  For example, the numerical values, structures, substrate raw materials, processes, and the like given in the above-described embodiments are merely examples, and different numerical values, structures, substrates, raw materials, processes, and the like may be used as necessary.

Specifically, as the host layer, three types of ZnCdSe, MgSe / ZnCdSe, and MgZnCdSe were cited in the embodiment, but Mg _x Zn _y Cd _1-xy Se, Be _u Zn _v Cd _1- uv Any of Se, Mg _a Zn _1-a Se _b Te _1-b , Be _c Zn _1-c Se _d Te _1-d (0 <x, y, u, v, a, b, c, d <1) But you can.

  Specifically, the host layer has a superlattice structure, MgSe / ZnCdSe, MgSe / ZnSeTe, MgSe / BeZnCdSe, MgSe / BeZnSeTe, MgZnBeTeSe / ZnCdSe, MgZnBeTeSe / ZnSeTe, MgZnTeTeBnTeTe, MgZnTeTeBnTeTe. It may be.

  Specifically, the host layer includes a material containing S as group VI atoms and Cd as group II atoms at the same time.

Specifically, as the specific layer, ZnTe and ZnSeTe are mainly exemplified in the embodiment, but ZnTe, ZnSe _f Te _1-f , Be _g Zn _1-g Te, Mg _p Zn _1-p Se. It may be composed of either _q Te _1-q or BeTe (0 <f, g, p, q <1).

  More specifically, in the embodiment, the specific layer thickness is 0.73 nm in ZnTe. However, the layer thickness may be 2 ML or more, that is, it may be 0.61 nm or more in ZnTe.

  Specifically, the specific layer does not describe the growth shape of ZnTe in the embodiment, but it is either a layered growth or a dot-like (island-like) growth. But you can.

  Further, specifically, the present invention is characterized in that the carrier concentration is increased by an order of magnitude or more compared to the case of a host layer alone (in the case of not having a specific semiconductor layer).

Specifically, as included in the present invention, in a compound semiconductor layer mainly composed of Group II and Group VI atoms having Eg (energy gap)> 2.9 eV, a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or more is present. It is characterized by being obtained.

  Specifically, the present invention includes a compound semiconductor layer mainly composed of Group II and Group VI atoms having Eg (energy gap)> 2.9 eV, and a dopant activation rate of 5% or more is obtained. It is characterized by being able to.

  Further, in the embodiment, in order to obtain a desired carrier concentration in the host layer, the dopant is introduced into both the host layer and the specific layer, but this may be a method in which only one of the dopants is introduced.

  Specifically, in the case where distortion occurs due to the host layer and the specific layer to be inserted, this includes compensating the entire distortion of the semiconductor layer by intentionally shifting the lattice of the semiconductor layer from the substrate.

  Further, in the embodiment, it is described that a specific semiconductor layer is inserted on a semiconductor substrate made of InP to obtain a desired carrier concentration in the host layer. However, as the substrate, GaAs, GaP, ZnSe, ZnTe, Si , Ge, sapphire, GaN, SiC, or the like.

  In the embodiment, the semiconductor LD is used as the light emitting element. However, the light emitting diode and the light receiving element include PD.

It is the 1st conception schematic diagram of the present invention, and is a figure showing the structure by the present invention typically, and is a sectional view of the structure where a specific layer was inserted in the host layer. It is a figure which shows the energy gap and lattice constant of a related compound semiconductor for demonstrating this invention. It is a 2nd conceptual schematic diagram of this invention. (A), (b) shows the valence band structure of the semiconductor which inserted the specific layer in the host layer typically. It is a figure explaining the theoretical basis of this invention, and is a model which shows the valence band structure of the quantum well which inserted the specific layer in the host layer, the p-type carrier (hole) which exists there, its wave function, and an energy level FIG. It is a figure for demonstrating the laminated structure of the host layer which has a fixed film thickness, and a specific layer in the 1st Embodiment of this invention. It is a figure for demonstrating the laminated structure made into the film thickness modulation structure which changes the film thickness of both the host layer and the specific layer regularly in the 1st Embodiment of this invention. It is a graph which shows the relationship between the effective acceptor density | concentration of the ZnCdSe / ZnTe superlattice obtained by the 1st Embodiment of this invention, and the ZnTe layer thickness in one superlattice period. (A)-(d) demonstrates the other application example of the laminated structure made into the film thickness modulation structure which changes the film thickness of both a host layer and a specific layer regularly in the 1st Embodiment of this invention. FIG. (A)-(d) is a figure which shows the energy with respect to the lamination direction obtained by the laminated structure in FIG. 7A (a)-(d), respectively. (A), (b) is a figure for demonstrating the two structural examples of the 2nd Embodiment of this invention. It is the graph which showed the relationship between the effective acceptor density | concentration of the MgSe / ZnCdSe / ZnTe superlattice in the 2nd Embodiment of this invention, and the MgSe layer thickness in one superlattice period. It is a graph which shows the relationship between the forbidden band width of the MgSe / ZnCdSe / ZnTe superlattice in the 2nd Embodiment of this invention, and the MgSe layer thickness in one superlattice period. It is a figure for demonstrating the laminated structure of the host layer which has a fixed film thickness, and a specific layer in the 3rd Embodiment of this invention. It is a figure which shows the relationship between the energy gap and carrier concentration of the MgZnCdSe / ZnTe superlattice in the 3rd Embodiment of this invention. It is a figure for demonstrating the semiconductor laser structure of the 4th Embodiment of this invention. It is a figure which shows the energy with respect to the lamination direction obtained by the laminated structure in FIG. 13A. It is a figure for demonstrating the first half part of the general procedure which forms each optical semiconductor device from the epitaxial wafer demonstrated in FIG. It is a figure for demonstrating the latter half part of the general procedure which forms each optical semiconductor device from the epitaxial wafer demonstrated in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Host layer (MgZnCdSe layer), 2 ... Specific layer (ZnSeTe layer), 11 ... Host layer (MgSe / ZnCdSe superlattice layer), 12 ... Specific layer (ZnSeTe layer), 21 ... InP substrate, 22 ... InP buffer layer 23 ... InGaAs buffer layer, 24 ... ZnCdSe low temperature buffer layer, 25 ... ZnCdSe buffer layer, 26 ... MgSe / ZnCdSe superlattice, 28 ... ZnCdSe / ZnTe superlattice, 30 ... ZnTe layer, 31 ... Schottky type two electrodes, 34 ... specific layer (ZnTe), 35 ... ZnCdSe layer, 36 ... MgSe layer, 41 ... ZnTe layer, 42 ... ZnCdSe layer, 43 ... MgSe layer, 45 ... MgZnCdSe layer, 46 ... specific layer (ZnTe), 47 ... Cl doped n-type MgZnCdSe cladding layer, 48 ... MgZnCdSe barrier layer, 49 ... BeZnCdSe Child well active layer, 50 ... ZnSeTe / ZnTe contact layer, 53 ... InGaAs buffer layer, 54 ... ZnCdSe low-temperature buffer layer, 55 ... ZnCdSe buffer layer, 100 ... epitaxial wafer, 101 ... light emitting part, 102 ... base, 103 ... wafer 104 diamond cutter, 105 chip, 106 Si submount, 107 heat sink stem, 108 window cap.

Claims (20)

An n-type cladding layer, an active layer and a p-type cladding layer on an InP substrate;
The p-type cladding layer has a first layer and a second layer,
As the first layer, at least one of the following (a) to (e) is used:
(A) MgZnCdSe layer,
(B) a superlattice having a MgSe layer and a ZnCdSe layer;
(C ) a layer comprising B eZnCdS e ;
It is those using a superlattice having a (d) MgSe layer and the ZnSe layer, Be the MgSe layer, includes the case that at least one of Z n, Be the ZnSe layer, Cd, at least the M g Including the case of containing one,
(E) A II-VI group material is used as the first layer, the group II material has Cd, the group VI material has S, and the first layer is a single layer. Is or is a layer of a superlattice,
An optical semiconductor device using at least one of a ZnSeTe, ZnBeTe, ZnTe, MgZnSeTe, or BeTe layer as the second layer. 2. The light according to claim 1, wherein the p-type carrier concentration of the layer having the first layer and the second layer is 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ²² cm ⁻³ or less. Semiconductor device. An n-type cladding layer, an active layer and a p-type cladding layer on an InP substrate;
The p-type cladding layer has a first layer and a second layer,
MgZnCdSe is used as the first layer,
An optical semiconductor device using ZnSeTe as the second layer. 4. The light according to claim 3, wherein the p-type carrier concentration of the layer having the first layer and the second layer is 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ²² cm ⁻³ or less. Semiconductor device. An n-type cladding layer, an active layer and a p-type cladding layer on an InP substrate;
The p-type cladding layer has a first layer and a second layer,
Using a superlattice having MgSe and ZnCdSe as the first layer,
An optical semiconductor device using ZnSeTe as the second layer. 6. The light according to claim 5, wherein a p-type carrier concentration of the layer having the first layer and the second layer is 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ²² cm ⁻³ or less. Semiconductor device. An n-type cladding layer, an active layer and a p-type cladding layer on an InP substrate;
The p-type cladding layer has a first layer and a second layer,
As the first layer , B eZnCdS e is used,
An optical semiconductor device using ZnSeTe as the second layer. 8. The light according to claim 7, wherein a p-type carrier concentration of the first layer and the layer having the second layer is 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ²² cm ⁻³ or less. Semiconductor device. An n-type cladding layer, an active layer and a p-type cladding layer on an InP substrate;
The p-type cladding layer has a first layer and a second layer,
MgZnCdSe and BeZnCdSe are used as the first layer,
An optical semiconductor device using at least one of ZnTe, ZnBeTe, MgZnSeTe, or BeTe as the second layer. 10. The light according to claim 9, wherein the p-type carrier concentration of the layer having the first layer and the second layer is 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ²² cm ⁻³ or less. Semiconductor device. An n-type cladding layer, an active layer and a p-type cladding layer on an InP substrate;
The p-type cladding layer has a first layer and a second layer,
Wherein as the first layer, there is used a superlattice having an MgSe layer and a ZnSe layer, Be the MgSe layer, it includes the case that at least one of Z n, Be the ZnSe layer, Cd, It includes the case of containing at least one M g,
An optical semiconductor device using a ZnSeTe material as the second layer. 12. The light according to claim 11, wherein the p-type carrier concentration of the layer having the first layer and the second layer is 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ²² cm ⁻³ or less. Semiconductor device. An n-type cladding layer, an active layer and a p-type cladding layer on an InP substrate;
The p-type cladding layer has a first layer and a second layer,
Wherein as the first layer, there is used a superlattice having an MgSe layer and a ZnSe layer, Be the MgSe layer, it includes the case that at least one of Z n, Be the ZnSe layer, Cd, It includes the case of containing at least one M g,
An optical semiconductor device using at least one of ZnBeTe, ZnTe, MgZnSeTe, or BeTe layer material as the second layer. 14. The light according to claim 13, wherein the p-type carrier concentration of the layer having the first layer and the second layer is 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ²² cm ⁻³ or less. Semiconductor device. An n-type cladding layer, an active layer and a p-type cladding layer on an InP substrate;
The p-type cladding layer has a first layer and a second layer,
As the first layer, a II-VI group material is used, the group II material has Cd, the group VI material has S, and the first layer is a single layer,
An optical semiconductor device using at least one of ZnSeTe, ZnBeTe, ZnTe, MgZnSeTe, or BeTe layer material as the second layer. 16. The light according to claim 15, wherein the p-type carrier concentration of the layer having the first layer and the second layer is 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ²² cm ⁻³ or less. Semiconductor device. An n-type cladding layer, an active layer and a p-type cladding layer on an InP substrate;
The p-type cladding layer has a first layer and a second layer,
As the first layer, a II-VI group material is used, the group II material has Cd, the group VI material has S, and the first layer is a superlattice layer,
An optical semiconductor device using at least one of ZnSeTe, ZnBeTe, ZnTe, MgZnSeTe, or BeTe layer material as the second layer. 18. The light according to claim 17, wherein the p-type carrier concentration of the layer having the first layer and the second layer is 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ²² cm ⁻³ or less. Semiconductor device. An n-type cladding layer, an active layer and a p-type cladding layer on an InP substrate;
The p-type cladding layer has a first layer and a second layer,
As the first layer, a material of Mg _x Zn _y Cd _1-xy Se is used,
As the second layer, at least one of ZnSeTe, ZnBeTe, ZnTe, MgZnSeTe, or BeTe layer material is used,
The composition ratio (x, y) of the Mg _x Zn _y Cd _1-xy Se layer is y = 0.47−0.37x (x = 0 to 0.8, y = 0.47 to 0.17). An optical semiconductor device characterized in that the composition ratio is in the range of (x = 0, y = 0.47) to (x = 0.8, y = 0.17) in a combination satisfying the relational expression: 20. The light according to claim 19, wherein the p-type carrier concentration of the layer having the first layer and the second layer is 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ²² cm ⁻³ or less. Semiconductor device.

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